1. Field of the Invention
The present invention relates to an ink jet recording material. More particularly, the present invention relates to an ink jet recording material having not only an excellent ink jet recording performance but also a superior offset printing adaptability.
2. Description of the Related Art
An ink jet recording system using an aqueous ink is advantageous in that printing noise is low, full colored images can be easily recorded, and the recording can be effected at a high speed, and the application of the ink jet recording system has progressed in many fields including, for example, terminal printers for computers, facsimile machines, plotters, and book and slip-printers.
Conventional woodfree paper sheets and coated paper sheets for usual printing are insufficient in ink absorption, and thus the ink images printed on the conventional paper sheet surface are kept in an undried condition for long time, the printer and printing paper sheets are stained by the undried ink images and the printed ink images are also soiled. Therefore, the conventional printing paper sheets are inadequate for ink jet recording in practice.
As a means for solving the above-mentioned problem, Japanese Unexamined Patent Publication No. 52-53,012 discloses a recording paper sheet, having a low sizing degree, usable as an ink jet recording sheet, and Japanese Unexamined Patent Publication No. 53-49,113 discloses an ink jet recording sheet prepared by impregnating a paper sheet containing a urea-formaldehyde resin, with a water soluble polymer. Also, for the purpose of enhancing colored ink image-forming properties and reproducibility of the colored ink images, various recording sheets having a recording surface layer formed by coating various porous inorganic pigments, for example, amorphous silica pigments are disclosed in Japanese Unexamined Patent Publication No. 55-51,583 and No. 56-148,585.
For the purpose of forming colored ink images having a high accuracy by preventing spreading of the ink, Japanese Unexamined Patent Publication No. 58-110,287, No. 59-185,690 and No. 61-141,584 disclose various porous pigments, having improved specific physical properties, usable for the ink jet recording sheets.
Further, Japanese Unexamined Patent Publication No. 55-150,396 discloses a method of imparting a cationic polymer and a water-soluble metal salt capable of reacting with a dye contained in an ink to form a water-insoluble metal lake, to recorded ink images on an ink jet recording material, to prevent blotting of the ink when the recording material is wetted with water. For the same purpose as mentioned above, Japanese Unexamined Patent Publication No. 56-84,992 discloses an ink jet recording material in which a recording layer contains a polycationic polymeric electrolyte, and Japanese Unexamined Patent Publication No. 60-161,188 discloses an ink jet recording material of which a recording surface is coated with a resin type dye-fixing agent or the like.
Currently, due to a significant development of printing system, a new type of ink jet recording material having a high surface strength sufficient for high speed printing system, for example book and slip-printing system, and an excellent water-resistance is required. The images shown on the books and slips comprise fixed items, for example, background patterns, ruled lines, and addresses and variable items, for example, address and name, the number, and price of article. In a highly efficient practice, the fixed items are printed on the ink jet recording material by an offset printing system, and only variable items are printed by the ink jet recording system. Therefore, the ink jet recording material is required to have a satisfactory adaptability for offset printing.
To impart an excellent ink absorption to a recording surface of the ink jet recording material, an ink receiving layer in which a porous pigment, for example, a xerogel pigment, is fixed with an amount as small as possible of a binder is preferably formed on a support surface. When, as an ink jet recording material, a woodfree paper type sheet on which a recording coat layer comprising, as a main component, a pigment, is coated in a small thickness is employed, an enhanced resistance to the feathering phenomenon and a high ink absorption can be imparted to the woodfree paper sheet by controlling the ash content, the sizing agent added to the paper-forming slurry and the size-press. However, when only the ink jet recording adaptability is seriously considered, and the amounts of the binder and the size-press agent are excessively reduced, or the content of ash is excessively increased, the resultant ink jet recording material exhibits an insufficient surface strength and, thus, in the offset printing procedure, various problems, for example, partial peeling and blanket-piling, easily occur.
Where the fixed items and variable items are printed on an ink jet recording sheet, the fixed items are printed by offset printing and then the variable items are printed by an ink jet recording. In the offset printing, a printing blanket is brought, in such a condition that an ink is present on an image portion and wetting water is present on a non-image portion of the blanket, into contact with the recording surface of the recording sheet. In the printing procedure, the recording sheet surface rapidly absorbs the wetting water supplied from the blanket to the sheet surface in a first colored image printing step, and then is brought into contact with a blanket for a second colored image printing step. In this case, if the recording sheet surface has an insufficient surface strength, portions of the sheet surface are removed by the blanket. This phenomenon is referred to as a partial-peeling phenomenon. The removed portions of the paper sheet are successively accumulated on the blanket and, as a result, it becomes impossible to continue the printing. This phenomenon is referred to as a blanket piling phenomenon.
In the usual paper sheets for the offset printing, a sufficient surface strength for the offset printing can be easily imparted, and thus the above-mentioned phenomena substantially do not occur in practice. However, in the conventional ink jet recording paper sheet, the content of the binder contained in the ink receiving layer is kept at a low level to keep the ink-absorbing capacity of the ink receiving layer at a high level, and the adaptability of the resultant ink receiving layer to the offset printing has not been carefully considered. Therefore, when the conventional ink jet recording paper sheet is subjected to the offset printing, the problems of the partial-peeling phenomenon and the blanket-piling phenomenon occur.
Thus, the inventors of the present invention have noticed as follows.
In the conventional ink jet recording material, it has been difficult to attain both a satisfactory offset printing adaptability and an excellent water resistance of the ink jet images.
Also, as a binder for the ink receiving layer, a water-soluble binder is advantageously employed to enhance the ink absorption of the ink receiving layer. Further, with respect to the cationic polymer which is employed for the purpose of enhancing the water-resistance of the ink jet images, the water-resistance-enhancing effect of the cationic polymer increases with a decrease in molecular weight of the cationic polymer. The reason for this phenomenon has not yet been completely clarified. However, it is assumed that the solubility of the cationic polymer in the solvent medium of the ink increases with a decrease in the molecular weight of the cationic polymer, and thus the cationic polymer having a low molecular weight can be easily dissolved in the solvent medium of the ink and thus rapidly reacts with the dye in the ink.
Further, when the water-soluble resin for the binder of the ink receiving layer is employed in too large an amount, or when the cationic polymer used for the purpose of enhancing the water resistance of the colored images printed by the ink jet recording system has too low a molecular weight, the water-soluble resin and/or the cationic polymer is dissolved in the wetting water of the printing blanket, the dissolved binder and/or cationic polymer stains printing plate, blanket, and rolls of wetting water-supply device, and thus the recording sheet is also stained and the water-flow system is soiled. Thus, the printing per se is greatly affected.